Drying and dehumidifying method suitable for preserved fruits and application of drying and dehumidifying method

Abstract

The invention discloses a drying and dehumidifying method suitable for preserved fruits and application thereof, and the drying and dehumidifying method comprises the following steps: draining sugar from pickled preserved fruits, washing sugar, mixing with edible oil, carrying out three-stage gradient cooling and drying to reduce the water content of the preserved fruits to 12-16g / 100g, and then dehumidifying, spraying oil and packaging to obtain preserved fruit products. The method is suitable for drying small preserved fruits with the particle size of 6-20 mm.

Description

Technical Field

[0001] The present invention belongs to the technical field of preserved fruit production, and particularly relates to a drying and dehumidifying method applicable to preserved fruit and its application. Background Art

[0002] Preserved fruit, also known as candied fruit, is a kind of food made from fresh fruits through main processes such as pitting (removing seeds), pickling, and drying. It is bright, transparent, dry on the surface, slightly sticky, with a water content usually below 20%. It tastes soft, sweet and sour, and has always been loved by people.

[0003] Cranberries are a kind of berry rich in nutrients. The pulp contains abundant substances such as proanthocyanidins, ellagic acid, phenolic acids, and resveratrol, which have antibacterial effects; many studies have shown that cranberries can inhibit the infection of Helicobacter pylori and have good effects on preventing gastric ulcers, gastric cancer, and duodenal ulcers. In addition, the flavonoid compounds in cranberries have antioxidant functions in both in vivo and in vitro experiments. Especially, flavonols and proanthocyanidins have a preventive effect on atherosclerosis. Cranberries also have functions such as lowering blood pressure, preventing urinary tract infections, and preventing cardiovascular diseases, and have multiple health care functions such as laxative, cholesterol reduction, and antiviral. Therefore, they have been loved by more and more consumers. However, due to the production area limitation of cranberries, as well as their short shelf life and high preservation difficulty, more of them enter the consumers' vision as cranberry preserves and cranberry juice. Among them, cranberry preserves retain 90% of the nutrients in cranberries, with a taste close to that of cranberry fruits, good taste, and low calories, and have become an excellent snack for people after meals.

[0004] Chinese Patent CN110692792A discloses a cranberry dried fruit with an extended shelf life and its processing method, which is prepared from frozen cranberry fruits through processes such as puncturing, sugar pickling, drying, and oil mixing. During the puncturing process, the temperature is controlled at -10°C to -5°C.

[0005] Chinese Patent CN 113357883 B discloses a hot air - cold air two - stage drying method for preserved fruit. It uses hot air circulation to dry the preserved fruit. The free water in the preserved fruit becomes water vapor under the action of hot air and enters the hot air, and then a dehumidifier is used to discharge the moisture in the air to achieve pre - drying; then it is naturally cooled, so that the free water and bound water in the preserved fruit seep out. At the same time, a dry gauze is covered on the surface of the preserved fruit, and under the capillary action, it promotes the penetration of the moisture inside the preserved fruit to the surface and onto the gauze, which helps the uniform drying of the preserved fruit; finally, under the action of cold air and dehumidification, the preserved fruit is dehydrated and dried under uniform conditions close to the natural state. The dried preserved fruit obtained in this way will maintain good softness, uniform texture, and excellent taste.

[0006] However, the existing method for drying preserved fruits is to evaporate water statically in a closed space, and the water evaporation of preserved fruits is greatly affected by the position. In addition, during the drying process, the preserved fruits are in a static state, and the sugar on their surfaces will cause the preserved fruits to agglomerate together or adhere to the surface of the drying device, resulting in incomplete drying, low drying efficiency, and damage to the quality of the dried products. Therefore, it is necessary to provide a method for evenly drying preserved fruits. Summary of the Invention

[0007] In view of the above technical problems, the present invention provides a drying and dehumidifying method for preserved fruits and its application, which adopts low-temperature dynamic evaporation drying, and multiple-angle changes are carried out during the drying process, so that the water content of the finished preserved fruits is more uniform and the quality effect is better.

[0008] To achieve the above object, the present invention provides a drying and dehumidifying method for preserved fruits, including the following steps: (1) Sugar draining and sugar washing: Drain the sugar water in the pickled preserved fruits and wash the surface of the candied fruits with water to remove the excess sugar. (2) Oil spraying: Mix the preserved fruits with edible oil to obtain oil-containing preserved fruits. (3) Gradient drying: Gradient drying reduces the water content: Primary drying: Dry at 60-63 °C until the water content is 22-26 g / 100 g. Secondary drying: Dry at 55-58 °C until the water content is 16-20 g / 100 g. Tertiary drying: Dry at 50-53 °C until the water content is 12-16 g / 100 g. (4) Dehumidification: Dehumidify with cold air and disperse with oil spraying. (5) Packaging.

[0009] Preferably, during the water washing in step (1), spray water washing is adopted, the water spraying amount is 100-200 L / h, and stir while spraying water for washing. After washing, the sugar degree of the preserved fruits is 50-55 degrees.

[0010] More preferably, the water washing is to wash off the excess sugar solution on the surface of the preserved fruits, keep the shape of the preserved fruits unchanged, and reduce the surface viscosity; the washing water is recycled during the water washing, and the water is changed when the sugar degree ≥ 20 degrees.

[0011] Preferably, when the preserved fruits and the edible oil are mixed in step (2), spray mixing is adopted, and stir while spraying for mixing; wherein the oil spraying amount is 10-25 L / h.

[0012] More preferably, the mass ratio of the preserved fruits to the edible oil is 1000:2-3.

[0013] Even more preferably, the edible oil is any one of sunflower oil, corn germ oil, and soybean oil.

[0014] Preferably, in step (3), the humidity in the first-stage drying is 80 - 100%, and the wind speed is 2 - 4 m / s; the humidity in the second-stage drying is 60 - 90%, and the wind speed is 2 - 4 m / s; the humidity in the third-stage drying is 40 - 70%, and the wind speed is 2 - 4 m / s.

[0015] More preferably, the fan is turned on throughout the first-stage drying process; in the second-stage drying and the third-stage drying, the fan is turned on for 10 - 20 minutes and then turned off for 10 - 20 minutes.

[0016] Even more preferably, in the second-stage drying and the third-stage drying, the fan is turned on and off for 15 minutes each.

[0017] Preferably, during the first-stage drying, second-stage drying, and third-stage drying in step (3), the material is flipped 5 - 7 times.

[0018] Preferably, the conditions for cold air dehumidification in step (4) are 25 - 35°C, humidity 20 - 40%, and wind speed 2 - 4 m / s; for the oil spraying and dispersion, the oil is sprayed while the candied fruit material is being stirred and dispersed, and the oil spraying amount is 5 - 10 L / h.

[0019] The present invention also provides an application of the drying and dehumidification method suitable for candied fruits, and the application is in the drying of candied fruits.

[0020] Preferably, the candied fruit is a small-sized candied fruit with a particle size of 6 - 20 mm, and is preferably any one of cranberry candied fruit, apricot candied fruit, candied jujube, and preserved plum.

[0021] The beneficial effects of the present invention are as follows: By adopting the three-stage low-temperature dynamic drying technology, the candied fruits can be dried from multiple angles through the flipping of the candied fruits during each drying stage. On the premise of ensuring that the candied fruits maintain their original flavor and color, the consistency of the moisture content between candied fruit individuals is effectively controlled, the drying uniformity of the candied fruits is improved, and at the same time, agglomeration between candied fruits or adhesion between candied fruits and the drying device is avoided, reducing the impact on the drying quality of the product.

[0022] Through the three-stage low-temperature dynamic drying, the candied fruits have good texture and hardness, are full of chewiness, are neither overly dry and hard nor sticky due to high water content, and at the same time, the vitamins, minerals and other nutrients in the candied fruits are retained to the greatest extent.

[0023] By gradient control of the temperature, wind speed, and start-stop state of the fan in each drying stage, the energy consumption is reduced, thus saving the production cost and being suitable for industrial production.

[0024] By setting a certain interval time during the switching process between two adjacent drying stages, the process of cooling while dehumidifying is achieved for softening. In addition, when the previous drying stage ends and enters the next drying stage, conveyors, fabricators, etc. can be used to adjust the drying position of the preserved fruits, break them up, etc., further achieving multi-angle drying and improving the product uniformity. Description of the Drawings

[0025] Figure 1 It is the cranberry preserved fruit after sugar draining and sugar washing in Example 1.

[0026] Figure 2 It is the cranberry preserved fruit after three-stage drying in Example 1.

[0027] Figure 3 It is the cranberry preserved fruit prepared in Comparative Example 3. Detailed Embodiments

[0028] The technical solutions of the present invention will be further explained below in conjunction with the drawings and specific embodiments. It should be noted that the following embodiments are only the preferred embodiments of the present invention and should not be construed as limitations on the present invention. The protection scope of the present invention should be based on the content recorded in the claims. Modifications and substitutions made by those skilled in the art to the technical solutions of the present invention without creative efforts all fall within the protection scope of the present invention.

[0029] Example 1 (1) Sugar draining and sugar washing: Take the pickled cranberry fruits, drain the sugar by oscillation and then place them in a spray conveyor drum (the residence time of the cranberry fruits in the drum is 40 s). While conveying, spray water to wash off the sugar adhered to the surface of the cranberry fruits, so that the sugar content is 50 degrees, and the spraying amount of the sprayed water is 100 L / h; (2) Place the sugar-washed cranberry fruits in an oil-spraying drum, and spray sunflower oil while stirring to obtain oil-containing preserved fruits; the rotation speed of the drum is 50 Hz, the residence time in the drum is 40 seconds, and the spraying amount of sunflower oil is 12 L / h; (3) Send the oil-containing preserved fruits to an oven for gradient drying to reduce the water content: First-stage drying: Dry at 60 °C until the water content is 26 g / 100 g, the humidity during drying is 90%, the wind speed is 3 m / s, and the fan is turned on throughout the process; Second-stage drying: Dry at 55 °C until the water content is 20 g / 100 g, the humidity during drying is 80%, the wind speed is 3 m / s, and the fan is turned on for 15 min and then stopped for 15 min; Third-stage drying: Dry at 50 °C until the water content is 16 g / 100 g, the humidity during drying is 60%, the wind speed is 3 m / s, and the fan is turned on for 15 min and then stopped for 15 min; During each stage of drying, the cranberry preserves are flipped 7 times to prevent sticking. When switching from the previous drying stage to the next, the interval is 4 h, the ambient temperature is 40 °C, and the humidity is 50%. The thickness of the cranberry preserves during drying is 5 cm. (4)Send the dried cranberry preserves to a dehumidification chamber and perform cold air dehumidification at 25 °C, a humidity of 35%, and a wind speed of 2 m / s to obtain dehumidified cranberry preserves. (5)Send the cranberry preserves to an oil spraying drum, spray sunflower oil while stirring to obtain the finished preserves. The rotation frequency of the drum is 50 Hz, the residence time in the drum is 15 s, the mass ratio of sunflower oil to cranberries is 2:1000, and the spraying rate of sunflower oil is 20 L / h. The oil should be sprayed evenly and vertically, and the cranberries and edible oil are evenly mixed by the rolling of the drum. (6)Pack and seal the finished preserves to obtain the preserve product.

[0030] Example 2 (1)Drain sugar and wash sugar: Take the pickled cranberries, drain the sugar by oscillation and place them in a spray conveyor drum (the residence time of the cranberries in the drum is 50 seconds), spray water while conveying to wash off the sugar adhered to the surface of the cranberries, so that the sugar content is 53 degrees. The spraying rate of the spray water is 80 L / h. (2)Place the sugar-washed cranberries in an oil spraying drum, spray sunflower oil while stirring to obtain oil-containing preserves. The rotation speed of the drum is 40 Hz, the residence time in the drum is 40 seconds, and the spraying rate of sunflower oil is 10 L / h. (3)Send the oil-containing preserves to an oven for gradient drying to reduce the water content: First-stage drying: Dry at 63 °C until the water content is 22 g / 100 g, the humidity during drying is 100%, the wind speed is 4 m / s, and the fan is turned on throughout the process. Second-stage drying: Dry at 58 °C until the water content is 16 g / 100 g, the humidity during drying is 90%, the wind speed is 3 m / s, the fan is turned on for 15 min and then stopped for 15 min. Third-stage drying: Dry at 53 °C until the water content is 12 g / 100 g, the humidity during drying is 60%, the wind speed is 3 m / s, the fan is turned on for 15 min and then stopped for 15 min. During each stage of drying, the cranberry preserves are flipped 7 times to prevent sticking. When switching from the previous drying stage to the next, the interval is 5 h, the ambient temperature is 40 °C, and the humidity is 50%. The thickness of the cranberry preserves during drying is 4 cm. (4)Send the dried cranberry preserves to a dehumidification chamber and perform cold air dehumidification at 25 °C, a humidity of 35%, and a wind speed of 2 m / s to obtain dehumidified cranberry preserves. (5) Send the cranberry preserves to the oil - spraying drum, spray sunflower oil while stirring to obtain the finished preserves. The rotational frequency of the drum is 40 Hz, the residence time in the drum is 18 seconds, the spraying amount of sunflower oil is 24 L / h, and the mass ratio of sunflower oil to cranberries is 2:1000; (6) Package and seal the finished preserves to obtain the preserve product.

[0031] Example 3 (1) Drain and wash the sugar: Take the pickled cranberries, drain the sugar by oscillation and then place them in a spray - conveying drum (the residence time of cranberries in the drum is 60 seconds), spray water while conveying to wash off the sugar adhered to the surface of the cranberries, so that the sugar content is 55 degrees; the spraying amount of the spray water is 60 L / h; (2) Place the sugar - washed cranberries in an oil - spraying drum, spray sunflower oil while stirring to obtain oil - containing cranberry preserves; the rotational frequency of the drum is 30 Hz, the residence time in the drum is 60 seconds, and the spraying amount of sunflower oil is 7 L / h; (3) Send the oil - containing cranberry preserves to an oven for gradient drying to reduce the water content: First - stage drying: Dry at 61 °C until the water content is 24 g / 100 g, the humidity during drying is 100%, the wind speed is 3 m / s, and the fan is turned on throughout the process; Second - stage drying: Dry at 56 °C until the water content is 18 g / 100 g, the humidity during drying is 90%, the wind speed is 3 m / s, and the fan is turned on for 15 min and then off for 15 min; Third - stage drying: Dry at 51 °C until the water content is 14 g / 100 g, the humidity during drying is 70%, the wind speed is 3 m / s, and the fan is turned on for 15 min and then off for 15 min; During each stage of drying, the cranberry preserves are flipped 7 times to avoid sticking; when switching from the previous stage of drying to the next stage, the interval time is 6 h, the ambient temperature is 45 °C, and the humidity is 55%; the thickness of the cranberry preserves during drying is 3 cm; (4) Send the dried cranberry preserves to a dehumidification box, and carry out cold - air dehumidification at 25 °C, humidity 35%, and wind speed 2 m / s to obtain dehumidified cranberry preserves; (5) Send the cranberry preserves to the oil - spraying drum, spray sunflower oil while stirring to obtain the finished preserves. The rotational frequency of the drum is 40 Hz, the residence time in the drum is 25 seconds, the spraying amount of sunflower oil is 30 L / h, and the mass ratio of sunflower oil to cranberries is 3:1000; (6) Package and seal the finished preserves to obtain the preserve product.

[0032] Comparative Example 1 The method and steps are the same as those in Example 1, except that the third-stage drying in step (3) is omitted, and it is directly dried to a water content of 16 g / 100 g of the preserved fruit during the second-stage drying, thus obtaining the preserved fruit product.

[0033] Comparative Example 2 The method and steps are the same as those in Example 1, except that the third-stage drying in step (3) is changed to drying at 63 °C until the water content is 16 g / 100 g, thus obtaining the preserved fruit product.

[0034] Comparative Example 3 The method and steps are the same as those in Example 1, except that the third-stage drying in step (3) is changed to directly drying at 50 °C until the water content is 16 g / 100 g, thus obtaining the preserved fruit product.

[0035] Comparative Example 4 The method and steps are the same as those in Example 1, except that step (4) is omitted, and the dried cranberry preserved fruit is directly subjected to oil spraying and mixing, and then packaged to obtain the preserved fruit product.

[0036] Comparative Example 5 The method and steps are the same as those in Example 1, except that step (5) is omitted, and the dehumidified cranberry preserved fruit is directly packaged to obtain the preserved fruit product.

[0037] Comparative Example 6 The method and steps are the same as those in Example 1, except that step (2) is omitted, and the cranberry preserved fruit after sugar draining and sugar washing is directly subjected to third-stage drying to obtain the preserved fruit product.

[0038] Comparative Example 7 The method and steps are the same as those in Example 1, except that the blower is kept on throughout the second-stage drying and third-stage drying processes in step (3) to obtain the preserved fruit product.

[0039] Example 4 Take an appropriate amount of the preserved fruit products prepared in the above examples and comparative examples, place them in a clean and dry white porcelain plate, observe their properties, colors, impurities, and smell them with the naked eye under natural light, and then rinse the mouth with warm water and taste their flavors to conduct sensory evaluations. The sensory evaluation indexes are shown in Table 1, and the evaluation results are shown in Table 2: Table 1 Sensory evaluation indexes of cranberry preserved fruit

[0040] Table 2 Sensory evaluation form of cranberry preserved fruit

[0041] The results showed that the cranberry preserves prepared in Examples 1-3 had high sensory evaluation, with good gloss, moderate taste, good drying effect, and not easy to agglomerate. In Comparative Example 1, the moisture content was too high and the candied fruit was not firm enough. In Comparative Example 2, the moisture content was too high and the color of the candied fruit was too heavy. In Comparative Example 3, the moisture content was too high, the drying temperature was low, the drying time was long, and the energy consumption was large. The cranberry preserves prepared in Comparative Examples 4-6 had good initial drying degree and were not easy to agglomerate. However, due to insufficient spraying amount of oil, they were extremely easy to agglomerate after being stored for a period of time.

[0042] In Comparative Example 7, the fan of the oven was turned on throughout the process, and the prepared preserves were not much different from those in the examples, but the energy consumption was high; compared with Comparative Examples 2 and 3, the energy consumption of three-stage drying was 10%-20% lower than that of one-time drying, which could significantly help reduce the production cost.

Claims

1. A drying and dehumidifying method applicable to candied fruits, characterized in that: It includes the following steps: (1) Sugar draining and sugar washing: Drain the sugar water in the candied fruit after pickling, and wash the surface sugar with water; (2) Oil spraying: Mix the candied fruit with edible oil to obtain oil-containing candied fruit; (3) Gradient drying: Gradient drying reduces the water content: Primary drying: Dry at 60 - 63 °C until the water content is 22 - 26 g / 100 g; Secondary drying: Dry at 55 - 58 °C until the water content is 16 - 20 g / 100 g; Tertiary drying: Dry at 50 - 53 °C until the water content is 12 - 16 g / 100 g; (4) Dehumidification: Cool down and dehumidify with cold air, and spray and disperse the oil; (5) Packaging.

2. The drying and dehumidifying method for preserved fruits according to claim 1, characterized in that: During the water washing described in step (1), spray water washing is adopted, the water spraying amount is 100 - 150 L / h, stir and wash while spraying water, and the sugar degree of the candied fruit after water washing is 50 - 55 degrees.

3. A drying and dehumidifying method for preserved fruits according to claim 1, characterized in that: When the candied fruit described in step (2) is mixed with the edible oil, spray mixing is adopted, and stirring and mixing are carried out while spraying; wherein the spray amount of oil is 15-25 L / h.

4. A drying and dehumidifying method according to claim 3, characterized in that: The mass ratio of the candied fruit to the edible oil is 1000:2 - 3.

5. A drying and dehumidifying method for preserved fruits according to claim 4, characterized in that: The edible oil is any one of sunflower oil, corn germ oil, and soybean oil.

6. A drying and dehumidifying method applicable to preserved fruits according to claim 1, characterized in that: The humidity in the primary drying described in step (3) is 80 - 100%, and the wind speed is 2 - 4 m / s; The humidity in the secondary drying is 60 - 90%, and the wind speed is 2 - 4 m / s; The humidity in the tertiary drying is 40 - 70%, and the wind speed is 2 - 4 m / s.

7. A drying and dehumidifying method for preserved fruits according to claim 6, characterized in that: The fan is turned on throughout the primary drying process; in the secondary drying and tertiary drying, the fan is turned on for 10 - 20 min and then turned off for 10 - 20 min.

8. A drying and dehumidifying method for preserved fruits according to claim 1, characterized in that: During the primary drying, secondary drying, and tertiary drying processes described in step (3), the material is turned over 5 - 7 times.

9. A drying and dehumidifying method for preserved fruits according to claim 1, characterized in that: The conditions for the cold air dehumidification described in step (4) are 25 - 35 °C, humidity 20 - 40%, and wind speed 2 - 4 m / s; the spraying and dispersing of the oil means spraying and dispersing the oil while stirring the candied fruit material, and the oil spraying amount is 5 - 10 L / h.

10. Use of a drying and dehumidifying method for preserved fruits according to any one of claims 1-8, characterized in that: The application is for the drying of candied fruit with a particle size of 6 - 20 mm.

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